Inflammatory processes are increasingly appreciated to play a critical role in vascular remodeling. This proposal addresses the role of inflammation, and specifically the role of macrophages in the vascular remodeling that characterize hypoxic forms of pulmonary hypertension (PH). Observations in most forms of PH show that macrophages accumulate primarily in the adventitial and perivascular regions of the vessel. Strong preliminary data demonstrate that fibroblasts resident in the adventitia of PH vessels undergo significant metabolic changes leading to increases in intracellular NADH concentration and subsequent activation of the transcriptional repressor C-terminal binding protein 1 (CtBP1), a transcriptional redox sensor with high binding affinity for NADH. CtBP1 acts specifically to repress expression of anti-inflammatory genes including, hemoxygenase-1 (HMOX-1). These activated fibroblasts recruit and activate macrophages toward a pro- inflammatory/remodeling phenotype largely through IL6, STAT3, HIF1 signaling and induction of aerobic glycolysis. We propose that both the pro-inflammatory fibroblast and fibroblast activated macrophage phenotype in hypoxic PH is driven by CtBP1. During hypoxia and/or in conditions of aerobic glycolysis we have shown that NADH-activated CtBP1 acts as a transcriptional co-repressor and complexes with DNA-binding transcription factors and histone modification enzymes (HDACs, HMTs). CtBP1 therefore links the metabolic status of the cell to specific coordination of gene transcription and, as we have shown, exerts a dominant role in determining cell behavior. We now address the novel hypothesis that CtBP1 drives the pro-inflammatory functions of fibroblasts in PH, leading to fibroblast-mediated macrophage activation. The inflammatory environment, caused by the interaction of fibroblasts and macrophages, leads to PH and pulmonary vascular remodeling. Our approach relies on in vitro and in vivo studies using lung adventitial fibroblasts and primary na?ve macrophages from hypoxic cows, rodents, and human controls and PH patients, and novel genetically modified mice. AIM 1: Determine the role of CtBP1 in locking the fibroblast into a pro-inflammatory phenotype. AIM 2: Determine the role of CtBP1 in controlling the pro-inflammatory/pro-remodeling phenotype of fibroblast-activated macrophages. AIM 3: Determine whether CtBP1/HO-1 signaling can be targeted in a cell-type-specific manner in vivo to prevent or even reverse hypoxia-induced PH. Our investigations will ultimately provide key data in elucidating the role of inflammation as a cause/contributor, a bystander, or whether or when it is simply the end result of the disease process. This is a critica step to advance our understanding of chronic pulmonary vascular disease in order to significantly impact the clinical management of PH.